Parkinson's Disease - Levadopa (L-dopa)

Highlights	Diagnosis	Lifestyle Changes
Introduction	Treatment	Resources
Symptoms	Levadopa (L-dopa)	References
Risk Factors	Medications
Complications	Surgery

Levadopa (L-dopa)

Levodopa, or L-dopa, which is converted to dopamine in the brain, remains the gold standard for treating Parkinson's disease. The standard preparations (Sinemet, Atamet) combine levodopa with carbidopa, which improves the action of levodopa and reduces some of its side effects, particularly nausea. Levodopa can also be combined with benserazide (Madopar) with similar results, but Sinemet is almost always used in America. Dosages vary, although the preparation is usually taken in three or four divided doses per day. In 2004, the FDA approved a new oral form of carbidopa-levodopa (Parcopa) that dissolves on the tongue.

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Indications of Early Treatment Success or Failures

In general L-dopa has the following effects on Parkinson's disease:

It is most effective against rigidity and slowness.
It produces less benefit for tremor, balance, and gait.

In many patients, levodopa significantly improves the quality of life for many years. If symptoms do not improve after two or three months, one of the following reasons may account for the failure:

Other neurologic problems may be causing the symptoms.
Some Parkinson's patients have abnormalities in other brain sites that do not respond to L-dopa.
Sometimes patients are so depressed they cannot tell if the drug is beneficial or not. Only a series of physical examinations by the doctor will indicate that the drug is actually helping.

One study indicated that men may be less responsive to L-dopa than women, although this finding needs to be confirmed in further trials. The observation could also simply indicate that the disease progresses more swiftly in men. A 2005 study suggested that levodopa may protect against brain cell degeneration.

Toxic Effects

The toxic effects of levodopa with or without carbidopa are considerable.

Physical Side Effects. The physical side effects are as follows:

Low blood pressure. Low blood pressure is a common problem during the first few weeks, particularly if the initial dose is too high. The addition of extra supplements of carbidopa reduces this effect to some degree. The patient should drink lots of fluids and possibly increase salt intake to maintain normal blood pressure.
Arrhythmia. In some cases the drug may cause abnormal heart rhythms.
Gastrointestinal effects. Stomach and intestinal side effects are common even with carbidopa. Taking the drug with food can alleviate the nausea. It should be noted, however, that proteins interfere with intestinal absorption of levodopa, and some physicians recommend not eating any protein until nighttime in order to avoid this interference. The drug can also cause gastrointestinal bleeding.
Effects in the lung. Levodopa can cause disturbances in breathing function, although it may benefit PD patients who have upper airway obstruction. The mechanism of such actions is unclear.
Hair loss.